Peptide-Functionalized Click Hydrogels with Independently Tunable Mechanics and Chemical Functionality for 3D Cell Culture

Abstract

Click chemistry offers highly selective and orthogonal reactions that proceed rapidly and under a variety of mild conditions with the opportunity to create highly defined and multifunctional materials. This work illustrates a strategy where step-growth networks are formed rapidly via a copper-free, azide−alkyne click chemistry between tetrafunctional poly(ethylene glycol) molecules and difunctionalized synthetic polypeptides. The molecular weight of the polymer precursors (10, 15, or 20 kDa PEG) and the stoichiometry of reactive end group functionalities (1.5:1 to 1:1.5) provide control over the material cross-linking density, enabling elastic materials with tunable moduli (G′ = 1000−6000 Pa). A sequential photochemically activated thiol-ene chemistry allows subsequent functionalization of the network through reaction with pendant alkene moieties on the peptide. Because the thiol-ene reaction is light-driven, the degree of modification is directly related to the dosage of light delivered to the system (0−6 J cm−2). We exploit this feature to create complex biochemical gradients of multiple peptides with well-defined magnitude and slope throughout the three-dimensional (3D) network. Since both reactions can occur in the presence of cells, this material ultimately enables independent and in situ tuning of biochemical and biomechanical properties of biomaterial networks, suggesting an avenue to direct cell function throughout specific regions within a 3D material.

Design and Characterization of a Synthetically Accessible, Photodegradable Hydrogel for User-Directed Formation of Neural Networks

“…The results can be predicted using fundamental theories describing step-growth gelation. (23,35,36) While SPAAC coupling between DBCO and NBA drives gel formation, the presence of NBA in the final network structure can serve as a photolabile linker, allowing externally directed degradation of the gel by exposure to UV single-photon or NIR two-photon irradiation. Upon absorption of a photon, the NBA cleaves between the nitrogen and the tertiary carbon through an intramolecular reaction into an amide-terminate fragment and an aldehyde-terminated fragment (Figure 2a).…”

Diels−Alder Click Cross-Linked Hyaluronic Acid Hydrogels for Tissue Engineering

“…This click strategy tolerates cell encapsulation with high viabilities (>90% at 24 hours). As an extension of this study, De Forest et al enabled control over cross-link density and shear moduli of these SPAAC cross-linked PEG hydrogels 39 . By altering either the azide:cyclooctyne ratio, or the molecular weight of PEG, hydrogels were synthesized with tunable moduli ranging from 1000 -6000 Pa.…”

“…Anseth and co-workers developed a sequential click protocol relevant to both hydrogel synthesis and post-gelation modification 38,39,124 . Click cross-linked PEG hydrogels were first formed via CuAAC, as an extension of the method taken by Malkock et al 27 .…”

“…By altering either the azide:cyclooctyne ratio, or the molecular weight of PEG, hydrogels were synthesized with tunable moduli ranging from 1000 -6000 Pa. These SPAAC cross-linked PEG hydrogels have also served as patterning platforms for the immobilization of biological functionalities using thiol-ene click photocoupling 38,39 .…”

Hydrogel drug delivery system with predictable and tunable drug release and degradation rates

“…The ∼7-nm (10 kDa PEG) distance between nodes of the gels used here provides a porous gel (mesh size >5 nm) that for our purposes would not significantly retard diffusion of proteins of up to at least 100 kDa (10,11). The general approaches used for tethering drugs to hydrogels and for hydrogel syntheses are depicted in Scheme 2 A key reaction used in synthesis of the hydrogels described here is Cu-free azide-alkyne click chemistry, which has become a popular method for polymerizing hydrogels (14)(15)(16)(17)(18). In one format ( Fig.…”